This invention relates to ink jet printer maintenance systems and more particularly to an ultrasonically excited liquid wiper in a maintenance station for either a partial width array printhead or a full width array printhead, wherein printhead nozzles which fail to eject a droplet or ejects droplets exhibiting misdirectionality are serviced by a liquid wiper at the maintenance station, which is scanned across the printhead face containing the nozzles, while the cleaning liquid between the liquid wiper and printhead face is excited by a piezoelectric device to dislodge and remove any viscous plug of dried ink in the printhead nozzles.
A continuing problem with thermal ink jet printers is the drying of ink at the printhead nozzles, thus causing clogging or partially blocking the nozzles. The result of clogged nozzles is that droplets fail to be ejected or that droplets fail to follow the desired droplet trajectory to the recording medium. To overcome this, a maintenance station is commonly used whereby the printhead is capped or sealed in a high humidity environment to prevent or to greatly retard drying. Maintenance stations include the capability of exerting a vacuum to suck ink from the nozzles to clear the nozzles of dried ink or viscous plugs and to remove any air bubbles that may have accumulated or formed in the printhead. This sucking of ink by the maintenance station is generally referred to as priming. Periodic ejection of ink droplets from the nozzles while the printhead is at the maintenance station also clears the nozzles of dried ink and viscous plugs of ink.
Full width array printheads having 300 to 600 nozzles per inch or more present unique problems for maintenance because of the large numbers of nozzles. For example, a 12 inch wide printhead having 600 nozzles per inch would employ 7200 nozzles, each of which is susceptible of drying out or having ink dry on the printhead nozzle face adjacent one or more nozzles. It is not economically practical to re-prime all of the nozzles each time a few may become clogged or eject misdirected droplets, for too much ink is wasted. Many approaches have been undertaken by the prior art to maintain the operability of all of the nozzles in a full width array printhead, but none have utilized a translating, high frequency energized liquid wiper having the nozzle size similar to the printhead nozzle size to ultrasonically clean the nozzles as the liquid wiper is scanned across the printhead nozzle face.
U.S. Pat. No. 5,250,962 to Fisher et al. discloses a movable priming station capable of priming a portion of an extended array of nozzles at one time in an ink jet printhead by applying a vacuum to at least one nozzle located in the array. The movable priming station includes a support which is moved along the length of the nozzle array and a vacuum tube is attached to the support. One end of the tube functions as a vacuum port which confronts but is spaced from the nozzles, when the support is moved laterally along the nozzle array.
U.S. Pat. No. 5,117,244 to Yu discloses a device to cap a full width array, thermal ink jet printhead without the need of moving the printhead or the paper transport. The capping device has a resilient gasket which contains magnetic material and is attached to the printhead by a relatively thin flexible boot or sleeve. The paper transport is a belt adjacently spaced parallel to the face of the printhead containing the nozzle array. The transport belt is flat and has a steel bar disposed in sliding contact beneath the belt portion confronting the printhead. During operation of the printer, an electromagnet disposed on the printhead is energized, allowing the steel bar to attract the magnetic gasket and seal the gasket to the transport belt.
U.S. Pat. No. 5,304,814 to Markham discloses a sensor circuit and method for detecting the presence of an ink droplet ejected from an ink jet printhead. An integrator integrates the output of the sensor and a high gain amplifier amplifies the integrated signal to provide a sensor circuit output signal. When the droplet at least partially interrupts the light path, the integrated output signal indicates the presence or passage of the droplet. The circuit is preferably used to control a heating element of a thermal ink jet printhead by adjusting the power to the heating elements to assure its operation with a power adequate to eject a droplet.
Copending U.S. Ser. No. 08/047,931, filed Apr. 19, 1993, entitled "Wet-Wipe Maintenance Device For A Full-Width Ink Jet Printer", discloses a shuttle which travels on a track through a fixed path parallel the printhead surface containing an array of nozzles. Mounted on the shuttle are an applicator for applying a liquid to the nozzles and a vacuum device for applying a suction to the nozzles.